This description relates to a bag or pouch for storing foodstuff. More particularly, the present description relates to polymer-based bags or pouches adapted to enable the venting of steam pressure during the cooking of foodstuffs stored therein while maintaining a positive pressure inside the package.
The availability of prepared ready to cook foods packaged in microwavable bags and pouches has increased significantly during recent years. Typically the consumer must puncture the bag prior to cooking to allow the steam pressure created during cooking to vent out of the package. Not allowing the steam to escape often results in the package “exploding” which creates a mess in the oven. Food suppliers and processors continually attempt to provide increased convenience to the consumer relating to ease of cooking. The result is a trend towards self venting bags which eliminate the step by the consumer to manually pierce a hole or opening into the bag prior to cooking. The bags contain a vent system incorporated into the film. There are various patents in this domain. One system is to perforate a given number of very small holes into the bag, the size and number determined by the foodstuff to be packaged and the corresponding cooking time required. Over the small holes there is placed a thin plastic membrane providing a hermetic seal, but with an adhesive/pressure combination to allow this membrane to dislodge from the primary bag material as the steam pressure builds inside the bag allowing the steam to vent through the small holes at a controlled rate. This system functions well for both fresh and frozen foods and fresh produce, since a controlled atmosphere can be maintained in the package. The drawback with this process is the production equipment set up required to pierce the holes in the quantity required for the foodstuff and the application of the membrane on each package with the correct adhesive/pressure combination to enable release of the membrane relative to the size required to cover any given number of holes. Production speeds are reduced which negatively impact cost.
Another system is the lamination of two polymer films, end to end with a very small space between the two films over which a very thin membrane strip is laminated. The polymer film can be made into a bag or pouch and as steam pressure builds inside the package during cooking the thin membrane strip will rupture at a random point along the length of the strip in the package and allow the steam to vent out of the bag. Maintaining positive pressure inside the package is difficult since this mechanism does not provide for a controlled rate of steam venting. Maintaining positive steam pressure inside a package is desirable since high levels of steam optimize the cooking of the foodstuff and significantly reduces dehydration of the foodstuff. This process works relatively well with fresh and frozen foods, but does not work well for packaging of fresh produce since the thin membrane does not provide a sufficient gas barrier to control the atmosphere inside the package due to excessive gas exchange.
Another venting system available is to micro perforate the entire package with various quantities of holes based on the food stuff to be cooked and the corresponding cook time. This is the least effective system since moisture loss due to freezer burn cannot be controlled in the case of packaging frozen foods, and for the packaging of fresh produce the number of micro perforations required to allow sufficient steam venting does not necessarily correspond to the number of micro perforations required to provide the ideal atmosphere through controlled gas exchange inside the package to maximize product life of most vegetables.